Take the rhizome, chop it into manageable pieces, and roast it gently over low heat. After that, you are going to take this roasted turmeric, and put it in a mortar, use a pestle to grind the turmeric, grind either coarse or fine.
Why is the turmeric roasted? That is because the rhizomes may have some dormant pests invisible to the eye, and yet vulnerable to the heat, which are going to get destroyed by the roasting. This also fixes the colour of the turmeric, and once you have ground the powder, all you have to do is place it in an airtight glass jar, and store it in a cool dry place.
The turmeric powder is good for anywhere between 6 to 8 weeks, only if you continue to give the turmeric a regular airing, in the sun every 15 days.